I really wanted to get to the top of Snowdon under my own steam, but the weather just didn't cooperate so we went up by train. However I did do a six hour hike/scramble which tested my knees to the limit, starting and finishing at Beddgelert. I was exhausted by the end of it but felt elated that my knees had coped so well, without a twinge either during the walk or afterwards. The views were just incredible, I fully recommend it if you are going to North Wales, it is labelled a 'strenuous ' walk.
I'll let you know if I manage Hellvelyn this week, once again I think it will be the weather rather than my knees that will stop me.